A number of different applications of catadioptric imaging systems for far-field and near-field interferometric confocal microscopy have been described such as in U.S. patent applications Ser. No. 10/028,508, filed Dec. 20, 2001 [ZI-38], and No. 10/366,651, filed Feb. 3, 2003 [ZI-43] entitled “Catoptric And Catadioptric Imaging Systems;” U.S. Provisional Patent Application No. 60/447,254, filed Feb. 13, 2003 and U.S. patent application Ser. No. 10/778,371, filed Feb. 13, 2004 [ZI-40] both entitled “Transverse Differential Interferometric Confocal Microscopy,” U.S. Provisional Patent Application No. 60/448,360, filed Feb. 19, 2003 and U.S. patent application Ser. No. 10/782,057, filed Feb. 19, 2004 [ZI-41] both entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling;” U.S. Provisional Patent Application No. 60/448,250 and U.S. patent application Ser. No. 10/782,058, filed Feb. 19, 2004 [ZI-42] both entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy;” U.S. Provisional Patent Application No. 60/442,982, filed Jan. 28, 2003 and U.S. patent application Ser. No. 10/765,229, filed Jan. 27, 2004 [ZI-45] both entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter;” and U.S. Provisional Application No. 60/459,425, filed Apr. 1, 2003 and U.S. patent application Ser. No. 10/816,180, filed Apr. 1, 2004 [ZI-50] both entitled “Joint Measurement Of Fields Of Orthogonally Polarized Beams Scattered/Reflected By An Object In Interferometry.” The above-mentioned patent applications and provisional patent applications are all by Henry A. Hill and the contents are incorporated herein by reference in their entirety.
In each of the applications of catadioptric imaging systems for each of the cited U.S. patent applications and U.S. Patent Provisional Patent Applications, tight tolerances are placed on the manufacture of optical elements. In addition to the tolerances normally encountered in designing a diffraction limited imaging system, there are tolerances imposed by the interferometric confocal microscopy applications. The additional tolerances are for example on radii of curvature of certain lens elements with respect to radii of curvature of certain other lens elements and on relative locations of centers of curvature of lens elements.
The additional tolerances lead to improved performance of a catadioptric imaging system, e.g., with respect to increasing the average intensity of desired images by a factor of approximately 2 or more and reduced intensity of spurious beams by one or more orders of magnitude, and in addition make it possible to realize interferometric reduction of background fields. The interferometric reduction of background fields leads to a reduction of statistical errors. The increase in intensity of desired images and the reduction of statistical errors lead to an increase in signal-to-noise ratios and to a concomitant increase in through put of a metrology tool using the catadioptric imaging system. The interferometric reduction of background fields further leads to a reduction systematic errors. A consequence of the reduction of systematic errors is a reduction of the computational task required to invert arrays of interference signal values to a multi-dimensional image of an object.